Coating composition and its preparation



Patented Nov. 10, I936 UNITED STATES PATENT OFFICE COATING COMPOSITIONAND ITS PREPARATION No Drawing. Application December 29, 1934, SerialNo. 759,801

7 Claims. (Cl. 134 -17) This invention relates to a coating compositionand its preparation. It relates more particularly to an aqueous coatingcomposition or rubber latex coating composition of the sort that is tobe applied to sheet material or the like a number of times and that issupposed to dry smoothly and with proper amalgamation or merger of theseparately applied thicknesses. While not limited thereto, the coatingcomposition of the present invention is designed more particularly forfinishing the surface of artificial leather base or sheet material ofthe kind comprising a fibrous base, for instance, a felted fibrous base,itself impregnated with rubber latex or similar rubber or rubber-dikecomposition and dried. Indeed, the coating composition of the presentinvention can be used advantageously in coating or finishing artificialleathers intended for such exacting service as shoe-upper stock andcomprising a rubber-impregnated web of felted fibers fabricated fromrefined wood pulps on machinery of the papermaking type under conditionsleading to a web of good uniformity of texture and evenness of surface.

I have found that an aqueous coating composi tion comprisingwater-dispersed rubber, such as rubber latex solids, and water-solubleglue has many advantageous qualities for the coating or finishing ofvarious bases and more especially an artificial leather base comprisinga rubber-impregnated fibrous sheet. Indeed, such a composition lends toan artificial leather a surface reminiscent in many respects of the skinor enamel side of natural leather, particularly when its glue contentundergoes an after-tanning treatment with formaldehyde or otherinsolubilizing agent that develops maximum wet scuff-resistance thereinand when it contains glycerine as a flexibilizing agent that imparts amellow or pliant feel thereto as well as increases its flex enduranceand prevents migration thereinto of such glycerine as may have beenintroduced along with latex solids into the body of the artificialleather in the manner and for the purpose disclosed in my applicationSerial No. 575,164, filed November 14, 1931. I have further found thatit is most desirable to emulsify into the aqueous coating composition ina substantially non-separating state suificient water-immiscible butvolatile rubber solvent to swell the dispersed rubber particlesappreciably but short of inducing their coagulation. Through such use ofa rubber solvent in the composition, it is possible to gain suchimportant benefits as perfect amalgamation or welding of successivecoats even though each ting-out agent.

coat is substantially completely dried before the next one is applied soas to avoid otherwise existing running tendencies in the composition andattendant streakiness or blotchiness of surface.

Evidently the rubber solvent not only softens and 5 swells the dispersedrubber particles of the composition so as to transform them to astickier or tackier state, but softens an already deposited dried layerof composition so as to result in an autogenous weld between layers,each layer being in effect an increment that contributes to the maskingof surface blemishes on the base being coated and to the building up ofan adequately thick wear-resistant structure whose integrality isperhaps best shown by the fact that under scuff or abrasion tests thereis no observable tendency for peeling or separation between layers suchas would detract from the serviceability of a coated artificial leatherfor such uses,

e. g. shoe upper stock, as require high wet and dry scuff resistance.

1 shall now describe typical coating compositions answering the purposesof my invention and how they were prepared. It might be remarked thatthe compositions about to be described were prepared with a view towardbeing used in coating artificial leather of the general characterdisclosed in my already mentioned patent application Serial No. 575,164.According to that application, artificial leather is made byimpregnating a fibrous base with glycerinated latex and then drying theimpregnated base. That application dwells in particular upon the use ofa soft, highly absorbent base such as is fabricated on machinery of thepapermaking type from fiber furnishes containing largely refined butsubstantially unhydrated cellulose pulp, e. g. wood pulp of an alphacellulose content of at least about 93%. It further stresses the valueof the glycerine in developing the desired pliancy or mellowness in theartificial leather without detracting from its toughness and otherleatherlike qualities. When the coating compositions of the presentinvention are applied to such artificial leather, it is desirable tointroduce glycerine thereinto for the reasons already indicated. Here isthe formula of a typical coating. composition in terms of itsnon-aqueous ingredients other than the rubber-swelling agent:

Per cent by weight Rubber latex solids 72 Glue 16 Glycerine 10 Remainderblack dye, anti-oxidant and a wet- The composition contains additionally75% by weight of toluol, based on all of its non-aqueous ingredientsexclusive of the toluol. The total water content of the finishedcomposition may be adjusted so that it contains about 15% by weight ofall non-aqueous ingredients exclusive of the toluol. In addition to theadvantages already mentioned, it has been found that the compositiondeposits smoothly on the artificial leather base, probably because thetoluol tends to dissolve such greasy or other surface-resistantimpurities as would otherwise cause localized shedding and thinning outof the aqueous composition. The toluol also has a preservative efiect onthe composition, permitting the composition to be kept longer withoutputrefaction than is otherwise the case.

In preparing the foregoing composition, it is preferable first todeammoniate the usual, ammonia-preserved rubber latex of commerce usedas a principal raw material. Otherwise the addition of rubber solvent tothe rubber latex may cause undue thickening and subsequent coagulationto take place. Deammoniation of the latex may be effected by aerating ituntil substantially all of its ammonia content has been expelled.Substantially complete deammoniation of the latex may also be had withlittle danger of local coagulation by the addition thereto of such mildacids as citric, oleic, lactic, oxalic, etc. However, deammoniation ofthe latex by aeration is preferable in that such practice avoids aninfusion into the latex of bodies that may be undesirable therein evenin such small amount as attends substantial neutralization of theammonia content of ordinary ammonia-preserved latex of commerce. Theglycerine, dye, and anti-oxidant may be mixed directly into the latex.To this latex mixture is then added an aqueous solution of the gluecontaining stably emulsified therein the toluol, a suitable wetting-outagent, such as Nekal BX,.a sodium salt of a naphthalene sulphonic acidwith side chains, preferably being present in slight amount to enhancethe stability of the emulsion. The desired emulsion of toluol in theaqueous glue solution may readily be prepared by dissolving the glue andwetting-out agent in water, raising it to a temperature of, say, aboutF., and gradually adding the xylol to the solution with stirring. Theemulsion is gradually added with gentle stirring to the latex mixture.The viscosity of the final mixture slowly rises during the first hour ortwo as the rubber particles therein absorb and are swollen by the toluoland then remains substantially constant.

Another typical coating composition embodying my invention hassubstantially the following formula in terms of its non-aqueousingredients other than the rubber-swelling agent:

Per cent by weight Rubber latex solids 66.2 Glue 14.5 Glycerine 9.2Pigment 9.27 Wetting-out agent 0.5 Anti-oxidant 0.33

This composition also contains additionally 75% by weight of toluol,based on all of its nonaqueous ingredients exclusive of the toluol; andthe concentration of all the non-aqueous ingredients other than thetoluol in the finished composition is 15% by weight of the finishedcomposition. The composition may be prepared advantageously in the sameway as the first-named composition.

The formulae of the foregoing compositions are subject to considerablevariation. Thus, the volatile rubber solvent employed may be xylol,gasoline, benzol, or their equivalents. However, toluol has worked outwell in routine production because it is not too volatile at roomtemperature while possessing sufiicient volatility to be volatilizedwith suflicient rapidity in a current of warm air. In this connection,it might be noted that when artificial leather is repeatedly coated withthe composition of the present invention, it is repeatedly run through aclosed chamber in which currents of warm air are brought to play on eachcoating to dry it quickly so that a succeeding coating may be appliedthereover. Toluol not only gives satisfactory results in the foregoingcoating practice, but is reasonably cheap, not too hazardous from eithera fire or health standpoint, and lends itself to easy emulsification ashereinbefore described. It is possible to reduce or increase the amountof toluol in the compositions hereinbefore described but without anyparticular benefit. In any event, suificient rubber solvent is used toswell the dispersed rubber particles appreciably but far short ofinducing their coagulation. While the ratio between the rubber latexsolids and water-soluble glue in the composition is also subject toconsiderable variation, a composition intended for coating artificialleather preferably contains distinctly less glue than rubber latexsolids and, correspondingly, contains much less glycerine than rubbersolvent.

Despite the fact that the coating compositions of the present inventioncontain the very ingredients, namely, rubber and rubber solvent that goto make the viscous and extremely sticky mixtures or so-called rubbercements of the prior art, they are very fluent and in no way resemble inoutward appearance such rubber cements. It might be observed thatalthough the glue ingredient is primarily valued because of thequalities that it imparts to the dried coatings yielded by the coatingcomposition of the present invention, yet it serves additionally as aremarkably eificient emulsifying agent for the rubber solvent so thatthere is no tendency whatever for the rubber solvent to separate outfrom the compositions. In using the term glue herein and in the appendedclaims, it should be understood that I mean to include albuminoussubstances, such as blood albumen, constituting equivalents of glue.

I claim:-

1. An aqueous coating composition of a freely fluent charactercomprising water-dispersed rubber, water-soluble glue, and glycerine andcarrying emulsified therein in a substantially non-separating statesuficient water-immiscible but volatile rubber solvent to swell thedispersed rubber particles appreciably but short of inducing theircoagulation,

2. An aqueous coating composition of a freely fluent character whoseprincipal solid constituents are rubber latex solids in water-dispersedcondition and water-soluble glue in amount distinctly less than saidrubber latex solids and whose principal liquid ingredients, other thanwater, are glycerine and water-immiscible but volatile rubber solventemulsified therein in a substantially non-separating state and insuincient amount to swell the dispersed rubber par- 2,060,129 4.3 ticlesappreciably but short. of inducing their coagulation.

3. An aqueoeus coating composition of a freely fluent character whoseprincipal solid constitucuts are rubber latex solids in water-dispersedcondition and water-soluble glue in amount distinctly less than saidrubber latex solids and whose principal liquid ingredients, other thanwater, are glycerine and a decidedly greater amount of water-immisciblebut volatile rubber solvent emulsified therein in a substantiallynonseparating state and in sufiicient amount to swell the dispersedrubber particles appreciably but short of inducing their coagulation.

4. A method of preparing a rubber latex coating composition containingadded water-soluble glue glycerine, and a water-immiscible rubbersolvent, which comprises first stably emulsifying the water-immisciblerubber solvent in an aqueous solution of the glue, and mixing theresulting emulsion with rubber latex and glycerine.

5. A method of preparing from ammonia-preserved rubber latex a rubberlatex coating composition containing added water-soluble lue and awater-immiscible rubber solvent, which coinprises substantiallycompletely deammoniating the ammonia-preserved rubber latex, emulsifyingthe water-immiscible rubber solvent in an aqueous solution of the glue,and mixing the resulting emulsion with the deammoniated rub ber latex.

6. An aqueous coating composition of a freeely fluent charactercomprising water-dispersed rubber, water-soluble glue, and glycerine andcarrying emulsified therein in a substantially nonseparating state about75% by weight of a waterimmiscible rubber-swelling agent, based on allof the non-aqueous ingredients in the coating composition exclusive ofthe rubber-swelling agent.

7. A method of preparing from ammonia-preserved rubber latex a rubberlatex coating com position containing added. water-soluble glue and awater-immiscible rubber solvent, which com prises aerating theammonia-preserved rubber latex until it is substantialiy completelydeammoniated, emulsifying the water-immiscible rubber solvent in anaqueous solution of the glue, and mixing the resulting emulsion with thesubstantially completely deammoniated rubber latex,

MILTON O. SCHUR.

